This relates to the field of radio frequency (RF) circuits and, more particularly, to matching networks in RF circuits.
An antenna of a radio frequency circuit may have varying admittance values, depending on the electrical environment around the antenna. Admittance has a complex numerical value consisting of a real conductance and an imaginary susceptance. For example, an antenna in a cellular phone may have one value of admittance when the cellular phone is held close to a human body and a different admittance value when the phone is on a table. The RF circuit may include a matching network between the antenna and another component, such as a transmission line, of the RF circuit coupled to the antenna. The matching network may reduce power losses due to reflected waves caused by an admittance mismatch between the antenna and the component coupled to the antenna. It may be desirable to tune the matching network so as to reduce the admittance mismatch as the antenna admittance varies. It may further be desirable to tune the matching network quickly and to employ low cost circuitry to perform the tuning.